Cell division is the fundamental process by which all living things grow and reproduce. In unicellular organisms such as yeast and bacteria, each cell division doubles the number of organisms, while in multicellular species many rounds of cell division are required to produce a new tissue or organ and to replace cells lost by wear or by programmed cell death. Details of the cell division cycle may vary, but the basic process consists of three principle events. The first event, interphase, involves preparations for cell division, replication of the DNA and production of essential proteins. In the second event, mitosis, the nuclear material is divided and separates to opposite sides of the cell. The final event, cytokinesis, is division and fission of the cell cytoplasm. Division and fission may involve formation of a constricting, longitudinal ring-like septum around the cell causing the mother/daughter cells to separate. The sequence and timing of these cell cycle events is under the control of the cell cycle control system which regulates the process at various check points. Over the past two decades, much research has been devoted to studying the structure and functions of various proteins that regulate these events.
The process of cytokinesis and septum formation has been well studied in plants, yeast, and insects. The septins are a family of proteins first identified in the budding yeast, Saccharomyces cerevisiae, that are involved in septum formation. (Longtine, M. S. et al., (1996) Curr. Opin. Cell Biol. 8:106-119). In yeast, four gene products (CDC3, CDC10, CDC11, and CDC12) are members of this family and are associated with the "bud filament" which is located directly inside the cytoplasmic membrane. Mutations in any of the CDC genes disrupts cytokinesis and gives rise to multinucleated cells with abnormal bud growth.
Homologs of the fission yeast CDC10 gene have been found in Candida albicans (CaCDC10), Drosophila melanogaster (Sep-1 and peanut), and human fetal lung (hCDC10) (DiDomenico, B. J. et al. (1994) Mol. Gen. Genet. 242:689-698; Fares, H. et al. (1995) Mol. Biol. Cell 6:1843-1859; Neufeld, T. P. and Rubin, G. M. (1994) Cell 77:371-379; Nakatsuru, S. et al. (1994) Biochem. Biophys. Res. Comm. 202:82-87). Sep1 is associated with the leading edge of the cleavage furrows of dividing cells and appears to have a role in furrow formation. Peanut is required for cytokinesis and imaginal disc formation in fly embryogenesis. Peanut is localized to the advancing membranes between syncytial nuclei in blastoderm embryos. In addition to a role in cytokinesis, the peanut gene displays genetic interactions with the fly gene seven in absentia required for neuronal fate determination in the compound eye (Neufeld and Rubin, supra).
Most of the septins share three domains rich in basic amino acids that are a common motif of GTP-binding proteins and of the GTPase superfamily. The first of these three domains, the sequence GXXGXGKST, is thought to be an ATP/GTP-binding and hydrolysis site (P-loop) that may be involved in septin assembly or function (Saraste, M. et al. (1990) Trends Biochem. Sci. 15:430-434). Two additional GTP-binding sites with the sequence DXXG(X).sub.n KXD (where n is approximately 78 amino acid residues) are present in some of the CDC1O homologs (Nakatsuru et al., supra). Cytokinesis is believed to be mediated by the filaments and other components formed from GTP-binding proteins. Most of the known septins also contain predicted coil-coiled domains of 35 to 98 amino acids near their C-termini (Longtine et al., supra). These domains may be involved in homotypic or heterotypic interactions among the septins themselves and/or with other proteins.
Progression through the cell cycle, and consequently cell proliferation, are governed by the complex interactions of protein complexes composed of cyclins, cyclin-dependent protein kinases, and associated proteins (Cordon-Cardo, C. (1995) Am. J. Pathol. 147:545-560). Cancers are characterized by uncoordinated cell proliferation and some cancers can be identified by changes in the protein complexes that normally control progression through the cell cycle (Nigg, E. A. (1995) BioEssays 17:471-480). A primary treatment strategy for cancer involves reestablishing control over cell cycle progression by manipulation of the proteins involved in cell cycle control (Neubauer, A. et al. (1996) Leukemia 10:S2-S4). For example, Cordon-Cardo (supra) suggested that negative regulators of Cdk4 may act as tumor suppressors.
Experiments with breast cancer and erythroleukemia cells show that certain agents which halt cell growth are probably acting through inhibition of Cdk4 activity (Watts, C. K. et al. (1995) Mol. Endocrinol. 9:1804-1813; Marks, P. A. et al. (1994) Proc. Natl. Acad. Sci. 91:10251-10254). The TATA box-dependent transcription machinery is also a potential target for cancer therapy. For example, the tumor suppressor protein p53 represses the activity of promoters whose initiation is dependent on the presence of a TATA box (Mack, D. H. et al. (1993) Nature 363:281-283). Furthermore, Mack, et al. (supra) observed that p53 repression is mediated by an interaction of p53 with basal transcription factors.
Modulation of factors which act in the coordination of the human cell division cycle may provide an important means to reduce tumorgenesis. Thus, new cell division cycle proteins which modulate these processes could satisfy a significant need in the art by providing new means of diagnosing and treating cancer.
The discovery of a new human growth-related CDC10 homolog and the polynucleotides encoding it satisfies a need in the art by providing new compositions which are useful in the diagnosis, prevention and treatment of neurological, reproductive, immunological, and neoplastic disorders.